resource hub | Cavity trays – major projects acceptance

Cavity trays – major projects acceptance

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Premier Guarantee will accept the use of non-combustible cavity tray products for warranty purposes on a project by project basis prior to provision of full third party certification. Below highlighted in green are acceptable subject to conditions. Highlighted in amber currently require further clarification for full acceptance. Highlighted in red are not currently acceptable for warranty purposes.

 

Inspections and approval

 

It is important that inspections are carried out by Façade Manager/MPM or MPS, the site manager and a representative of the manufacturer to confirm that the cavity trays are installed in accordance with manufacturers’ instructions. The trays should be inspected once they have been bedded on a mortar bed and prior to subsequent brickwork progressing. Bespoke water testing should be carried out when benchmarking. Whilst we may not insist on test conditions of 1.5litres/lm/min for up to three hours where brickwork is proposed, this should be agreed prior.

 

Universal requirements

 

  • Cavity trays are to be installed flush with the external face of the brickwork.
  • Cavity trays should be fixed against the sheathing board (with exception of IG Keyfix). Breather membranes should be subsequently dressed over the tray.
  • Cavity trays must be installed over a thin bed of mortar.
  • The cavity tray should have a minimum 140mm height from the inside face of the outer leaf. Cavity trays should be installed with a minimum 100mm vertical rise above points where mortar droppings could collect.
  • The cavity tray should be installed as close to the item it is protecting to a maximum 225mm above.
  • Non-combustible weep vents must be incorporated into the design. Ensure weeps are installed 225mm from inside of tray stop ends and at 450mm centres thereafter.
  • Minimum grade 304 steel, with 316 specified on coastal locations.
  • Seals – we are seeing varying sealing products specified. The tray should last the life of the wall. Products specified should be tested with guarantees provided along with site water testing highlighted at benchmark/mock-up stage.

 

Manufacturer Approval in principle? Caveats
ACS G-Tray YES Site specific designs required. This should include full details of laps/seals, fixings, corners/specials, weep vents. Structural engineer’s confirmation the movement expected is acceptable for each design (this should not be an issue when fixed to sheathing board only).
IG Keyfix YES Site specific designs required. This should include full details of seals, corners/specials, weep vents.
Structural engineer’s confirmation the movement expected is acceptable for each design (with exception of NCCT1).
Dorsey Stainless Steel Cavity Tray YES Site specific designs required. This should include full details of laps/seals, fixings, corners/specials, weep vents.
Structural engineer’s confirmation the movement expected is acceptable for each design (this should not be an issue when fixed to sheathing board only).
Visqueen Zedex non-combustible cavity tray YES Site specific designs required. This should include full details of laps/seals, fixings, corners/specials, weep vents.
Structural engineer’s confirmation the movement expected is acceptable for each design (this should not be an issue when fixed to sheathing board only).
The BBA are conducting the Factory Production Control (FPC) Certificate, i.e., auditing Visqueen batch control measures and verifying all testing. Although this is not a mandatory requirement of the CE mark, we await confirmation batches are controlled by a third party as agreed.
Metz – Zinc Cavity Tray NO Concern over zinc alkali in mortar with test evidence awaited.
Concern over Bi-metallic corrosion specifically in relation to aluminium.
Site specific designs required showing distance of laps/rolls, joints (concern over movement for long sections - structural engineer’s confirmation the movement expected can be tolerated)/seals/laps, stop ends, weeps, corner details, etc.
ENVIROGRAPH – Cavity Tray NO Product is satisfactory in terms of fire with several design considerations outstanding for cavity tray product acceptance.

 


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Every care was taken to ensure the information in this article was correct at the time of publication. Guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. For the most up to date Premier Guarantee technical guidance please refer to your Risk Management Surveyor and the latest version of the Premier Guarantee Technical Manual.